Accelerometer, gravity meter and gas flow responsive instrument



Apnl 26. 1966 Q YAVNE 3,247,723

ACCELEROMETER, GRAVITY METER AND GAS FLOW RESPONSIVE INSTRUMENT FiledJuly 20, 1964 2 Sheets-Sheet 1 DIFFERENTIAL AMPLIFIER Fig. 2b

F ig. BY RAPHAEL O YA\ /NE A TTORNEY April 26, 1966 R. o. YAVNEACCELEROMETER, GRAVITY METER AND GAS FLOW RESPONSIVE INSTRUMENT FiledJuly 20, 1964 2 Sheets-Sheet 2 INVENTOR RAPHAEL O. YAVNE ATTORNEY UnitedStates Patent 3,247,723 ACCELEROMETER, GRAVITY METER AND GAS FLQWRESPONSIVE INSTRUMENT Raphael 0. Yavue, 1001 Haral Place, Haddontowne,

Cherry Hill, NJ.

Substituted for abandoned application Ser No. 744,719, June 26, 1958.This application July 20, 1964, Ser. No. 386,811

' 7 Claims. (Cl. 73-516) This is a substitute application for US. patentapplication Serial No. 744,719, abandoned prior to July 20, 1964.

In its broadest sense, this invention relates to an instrument formeasuring the rate of flow of a gas past a point. More particularly,this invention relates to the utilization of this measurement principlein an accelerometer, gravity meter, or vertical measuring instrument.

Embodied as a gravity meter, this invention is useful for makingcomparative measurements of the force of gravity, commonly known as thegravity-constant and identified as g as it varies over different areasof the earth. A particularly valuable use of such a gravity meter is ingeodetic surveys and geological surveys, as in locating the salt domeswhich are often indicative of a subterranean deposit of'oil. Thepresence of subterranean structures such as salt domes produces slightvariations in g at that point as compared to g at other points on theearths surface. As will be seen, the physical characteristics of thisgravity meter makes it particularly suitable for underwater geologicalsurveys. This instrument has a high sensitivity for its weight and cost.The operative principle of this invention may be embodied in aninstrument which can measure gravity to within approximately l-millig alor better.

The principle herein disclosed may be embodied in an accelerometer, asis described below. The accelerometer may be made one, two or threedimensional. By

integrating the acceleration information supplied by theinstrument,velocity is determined; by double integration, distance travelled isdetermined. Such methods of handling accelerometer outputs are wellknown in the art. This accelerometer is useful in many fields ofnavigation, particularly'inertial and celestial navigationwhich haveexacting performance requirements. Accurate accelerometers are valuablein aircraft navigation and in the guidance of manned andunm-annedvehicles of all types, as well as in testing. This instrument may beembodied in a form so as to indicate deviation from a true verticalposition. Such an embodiment is valuable in providing stabilizedplatforms, which are useful in fire control and in navigation. Aparticular advantage of this instrument, in addition to its sensitivity,is the fact that it may be embodied in a physically small, light, simpleform, which is an extremely valuable attribute in many applications.

Throughout this specification, the instrument Will be described as anaccelerometer, since this is its broadest field of use and becausebroadly speaking, its other functions may be described as measurementsof acceleration. All accelerometers utilize the principle that differentmasses have different inertias. This is a broad description of theaccelerometer principle, but is believed to apply to all known typesincluding strain gauge accelerometers, or accelerometers usingpiezoelectric crystals. Broadly, this invention provides two differentmasses and a method and apparatus for transducing an acceleration actingon them. This apparatus and method provide great sensitivity andaccuracy'as well as advantage's in physical size, weight andreliability.

It is an object of this invention to provide a device and method formeasuring the flow of gases.

It is an object of this invention to provide two quantitles of gases ofdilferent masses and means to measure the effect of an acceleration orgravity on these masses and to translate said effect into an electricalsignal.

It is yet another object of this invention to provide a relatively hotmass of gas, a relatively cold mass of gas, a partition between saidmasses, twoparallel slots in said partition, a resistance wire in eachsaid gap, a means to provide a current in each said wire, and a means tomeasture the differential resistance of the said wires.

A still further object of this invention is to provide an accelerometerutilizing a differential heating and cooling effect on temperatureresponsive resistance wires.

A still further object of this invention is to provide a gravity meterutilizing a differential heating and cooling effect on temperatureresponsive resistance wires.

Yet another object of this invention is to provide a vertical-measuringinstrument utilizing a differential heating and cooling effect ontemperature responsive resistance wires.

Other objects and aims of this invention will be apparent from thedescription.

This invention is best understood in connection, with accompanyingdrawings wherein like reference numerals refer to like parts and inwhich:

FIGURE 1 is a simplified exploded perspective view of a 1-dimensionalembodiment of. this accelerometer.

FIGURE 2a is a schematic drawing of a bridge circuit used with thisaccelerometer;

FIGURE 2b is a schematic drawing of a temperature compensated bridgecircuit used with this accelerometer;

FIGURE 3 is a simplified perspective cutaway view of an embodiment ofthis invention in a 3-dimensional accelerometer;

FIGURE 4a is a cross-sectional view in detail of one embodiment of thegap or slot in the open position;

FIGURE 4b is a cross-sectional view in detail of one embodiment of thegap or slot in the closed or inoperative position; and

FIGURE 5 is a crosssectional view of one embodiment of thisaccelerometer utilizing certain refinements, and illustrating the closedgas circulatory system.

The general operation and construction of this invention is bestunderstood by reference to FIGURES l and 5. In FIGURE 1, a l-dimensionalaccelerometer is" shown generally at 1. The accelerometer consists oftwo chambers, 15 and 16, separated by a partition or dividing wall, 2.As shown by the phantom lines, the chambers are illustrated as explodedaway from the wall to better disclose the structure. The chamber on theleft, 15, as shown in FIGURE 1, is filled with a mass of hot gas, 3, andthe chamber on the right, 16, is filled with a mass of cold gas 4. 'Thepartition 2 has an upper slot or gap 5 connecting'the hot gas 3 and thecold gas 4. The partition 2 also has a lower gap of slot 6 which isspaced from and parallelto the upper gap and also connects masses 3 and4. It is understood that the terms upper and lower are merely convenientdesignations for the two slots. As shown in FIGURES 1 and 3, the

parallel slots are axially overlapping. The term axis parallel to upperwire 7. The upper resistance wire 7 i is connected to leads 8 and 9. Thelower resistance wire is connected to leads 11 and 12. A current ispassed through each of the wires 7 and 10.

The positioning of the upper and lower resistance wires with respect tothe partition is further clarified in FI G URE 5. In this figure, theupper resistance wire 36 is located within upper slot 41 and the lowerresistance wire is located within lower slot 37. The slots are providedin partition 47. It is seen that the wires are of smaller diameter thanthe width of the slots and are spaced away from the boundaries of theslots so as to permit the unimpeded flow of gas around the wires.Broadly, the wire may be described as adjacent to the slot and in athermally cooperating or responsive relationship to the temperaturewithin the slot. The relatively hot mass of gas is shown at 3 and therelatively cold mass of gas is shown at 4.

When the apparatus is operative and an acceleration is present the gasescirculate through the slots as shown by the broken arrow-headed lines inFIGURE 5. When the instrument is accelerating in the direction A, asshown in FIGURE 5, the direction of circulation of the gases is asindicated in the drawing. If the instrument is used as a gravity meter,the circulation would be as indicated if the mass whose gravity is to bemeasured is located above the figure, that is, if g is acting in thedirection opposite to that indicated for A.

The mass of the hot gas 3 in the chamber between the slots is less thanthe mass of the cold gas 4 between the slots. This is due, of course, tothe well known phenomenon of the expansion of gases, and consequentdecrease in density, as their temperature increases. When anacceleration acts on the instrument parallel to the partition 47 andperpendicular to the wires 41 and 42, it produces a different force onthe hot and cold gases because of their different masses and henceproduces a circulatory flow of the gases through the slots.

An electric current is passed through each wire and beats it to adesired temperature. Each wire, at this predetermined temperature, has aknown or easily determinable resistance. The important aspect is thatwhen there is no acceleration and hence no flow of gases, theresistances of the upper and lower wires are equal. As is well known,the resistance of a conductor is a function of its temperature; theresistance increasing With the temperature. When a flow of gas throughthe slots occurs, cold gas passes around one wire and hot gas passesaround the other wire. In FIGURE 5, under the acceleration as shown, hotgas passes through slot 37 and around wire 42 and cold gas passesthrough slot 36 and around wire 41. In FIGURE 1, assuming a downwardacceleration, the hot gas 3 passes through slot 6 and around resistancewire 10 and the cold gas 4 passes through slot and around resistancewire 7.

Thus, one of the resistance wires is further heated by the flow of a hotgas and the other resistance wire is cooled by the flow of a relativelycold gas. The wire over which the hot gas flows increases its resistanceand the wire over which the relatively cold gas flows decreases itsresistance. It is seen therefore, that a flow of gas, as is caused byacceleration or gravity, produces a differential between the resistancesof the two Wires. This differential resistance may be measured andamplified by means described below. The differential is an ifidex of themagnitude of the effect to be measured.

One pair of slots as described comprise an essentially l-dimensionalaccelerometer. A l-dimensional accelerometer is shown in FIGURE 1. Anacceleration parallel to the wall and perpendicular to the wires 7 and10 produces a first order differential in the resistances of the wires.An acceleration parallel to the wall and also parallel to the Wiresproduces no differential effect on the two wires. An accelerationperpendicular to both wall and wires produces no differential effect onthe two wires. The last named direction of acceleration does produce anequal flow past each wire causing an equal change in resistance. Byalgebraically adding the resistance changes of the two wires, the senseand magnitude of this acceleration can be determined, but this is only asec- 0nd order effect and does not affect any measurement ofdifferential resistance.

In FIGURE 1, the elements 13 and 14 schematically represent temperaturesensing and controlling means for the cold chamber 16 and hot chamber15, respectively. This accelerometer, subjected to any direction ofacceleration, will measure only that component acting in an up or downdirection.

It is desirable to minimize the mixing of the hot and cold gases duringoperation. Obviously, rapid mixing will destroy the predeterminedtemperature differential of the hot and cold gases. Therefore, thechambers should preferably be large to contain a large mass of each gasand the slots should be as narrow as possible to prevent excessivemixing. A minimum dimension of the slot width is determined by the pointat which the viscosity effects become large enough toexcessivelyinterfere with the gas flow through the slot.

An example of temperatures and dimensions that can be utilized is: thecold chamber at 0 C., the hot 'chamber at 10 C. and the wire normally at500 C. The upper temperature of the wire is limited by the material ofwhich it is made: a platinum wire could be maintained at a temperature.of about 1700 C.; a tungsten wire could be maintained at a temperatureof about 3800 C. The wire diameter could be of the order of 0.00l-inchand the slot width of the order of 0.0l-inch. The sensitivity of such anaccelerometer may be of the order of 1/10 or 1/ 10 g. Its time lag inresponding to an acceleration may be of the order of 1/10 seconds.

The gas used should preferably have a high coefficient of heat. Thus, agas of relatively high molecular weight is preferable. By putting thegas under high pressure, the heat carrying properties are still furtherincreased and therefore gas under pressure is preferable.

The rate of flow of the gas under acceleration can be further increasedby providing a gas of higher molecular weight for the cold chamber and agas of lower molecular weight for the hot chamber. Thus, the differencesin mass between the two quantities of gas will be further increased withan attendant increase in the sensitivity of the instrument.

Instead of the cold chamber being chilled below ambient temperature, itis possible to heat both chambers above the ambient temperature, but todifferent degrees. It is then possible to maintain the differentialtemperature by providing thermistors and heaters in each chamber.

Further refinements of the instrument may be made. In FIGURE 5, animproved accelerometer is illustrated. This embodiment shows chambers 32and 33 surrounded by liquid jackets 34 and 35, respectively. Theseliquid ackets are maintained at the desired temperature, thus permittinga more even provision of heat to the gas 3 and 4. Thermistors and 46 areprovided in each chamber respectively to set the temperature. Heatingelements 48 and 49 are provided respectively in each temperature to addheat as required.

A still further refinement is illustrated in FIGURES 4a and 4b. When theinstrument is not in actual operation, the slots may be closed toprevent mixing. A slide is provided adjacent to wall 47. The slide hasslots 53 and 54 which correspond in configuration to the slots 36 and 37in the wall. The slide is vertically movable, being held in placehorizontally by pin 49. The slide is free to travel vertically aroundthis pin because of slot 51.

The operation of the slide is schematically illustrated in FIGURES 4aand 412. A switch 58 closes a circuit so that current from source 57 canactivate rheostat 56 and hence move the slide 55. In FIGURE 4a, theslide is shown in its operative position so that its slots 53 and 54correspond with slots 36 and 37 and permit gas flow. In FIGURE 41), theslide is shown in its inoperative position, preventing gas flow throughslots 36 and 37. It is understood that this structure may be widelyvaried.

The accelerometer may be made Z-dimensional or Z-dimensional by theaddition of an additional pair or pairs of slots. A 3-dimensionalaccelerometer is illustrated in FIGURE 3 in which the instrument isgenerally indicated at 20. Right angled partition 21 separates theinstrument into two chambers. The partition comprises walls 22 and 23 atright angles to each other. The outer chamber is indicated at 31. Theouter chamber contains hot gas 3, temperature controlled by means 14.The inner chamber contains cold gas 4, temperature controlled by means13.

Three pairsof slots are provided as shown. The pairs are slots 26 and27; 24 and 25; and 28 and. 29. As explained above, each pairis effectivein one and only one direction or dimension. Thus, by the arrangement asshown, the instrument of FIGURE 3 is sensitive to acceleration in threedimensions. The omission of one pair of slots would produce a2-dimensional accelerometer. The information from the instrument may beinterpreted in any known manner.

FIGURE 2a schematically shows one method of measuring the differentialresistance. 77 and 78 are incorporated in a Wheatstone bridge andcurrent is supplied from source 81. Fixed resistances 79 and 80 areprovided as shown to-complete the bridge as is well known. Theresistance wires are positioned between points 74 and 75, and 73 and 75respectively and the known resistances are positioned between points 74and 76, and 73 and 76 respectively. Fixed resistance 71 and variableresistance 70 are provided between points 75 and 76 so that the circuitmay be prebiased in any desired manner. This permits measurement ofacceleration or gravity in any desired range. A galvanometer is providedacross the variable resistance 70 to indicate the differentialresistance and thus indicate the measured acceleration.

For further accuracy and sensitivity of the instrument, it is desirableto provide temperature compensation for possible variations in thetemperature differential of the two gas chambers. FIGURE 2bschematically illustrates a temperature compensating Wheatstone bridgeintended to be used with an alternating current. The resistance wires 60and 61 are positioned respectively between points 66 and 64, and 67 and64. The fixed bridge resistances 62 and 63 are positioned respectivelybetween points 66 and 65, and 67 and 65. A source of alternating currentis shown at 68 and supplies current across point 66 and 67. Resistancewires 82 and 83 vary respectively with the temperatures in the twochambers, and as shown in FIGURE 2b, act to compensate the circuit fortemperature variations in either or both chambers. A differentialamplifier 69 is provided as shown to amplify the A.C. differentialsignal.

Circuits are known in which the frequency of an AC. signal is varied asa function of resistance. If such a known circuit is used, thisinstrument may be used as an integrating accelerometer by counting thecycles of the difference frequencies.

It is desirable to keep the wire temperatures constant. By thus making anulling device of the instrument, as is well known, it is possible tomeasure larger gas flows without loss of linearity of the signal to thegas flow. It is obviously desirable to provide a linear output signal.

There are many possible combinations of hot and cold gas temperaturesand wire temperatures. There are also many possible gases andcombinations thereof, and a wide range of pressures, which can be used.The principle of this invention is operative throughout all thesepossible combinations of conditions, and the measurable effect 'will beproduced at least in some degree. It is obvious that the desiredcombination of conditions and materials will depend on the particularapplication. The preferable choice for a given application can betheoretically or experimentally determined by any competent worker inthe art.

The resistance wiresabove exist, the apparatus and method will beoperative.

One advantage of a cooled wire is that less heat supply is required.

Viscosity tends to oppose the flow of gas through the gaps and acrossthe wires. This viscosity of the flowing gas acts to damp the apparatusso that flow will cease upon the removal of acceleration or gravityeffects.

The quality of the instrument may be affected by varying the size of thegap. By making the gap very small, the viscosity effects are increased.This produces a slower time constant, and a low sensitivity. On theother hand, this reduction in sensitivity and increase in time constantmakes the instrument better suited for measurement of relatively high gaccelerations. Thus, a complete installation might include an instrumentadapted with small gaps for measuring high accelerations and aninstrument equipped with larger gaps for accurately measuring smalleraccelerations. It is apparent that the effective ranges of thisinvention may easily be controlled by varying the appropriate physicalcharacteristics, as has been described.

For increasing the viscous resistance to gas flow through the gaps, thewire may be provided in the form of a flat conductive ribbon, positionedin the same manner as the ordinary wire but with its lateral widedimension extending through the gap from the hot chamber side to thecold chamber side.

The instrument may be simplified for use in applications where itsoperative life is short and/ or where it will be destroyed or lost. Insuch applications, the gas masses can be initially brought to thedesired temperature and then used without further temperature controluntil mixing becomes too great for operation. Thus, heating or coolingapparatus need not be transported with the in strument during use.

A particularly novel feature of this principle is that the instrumentmeasures flow differentially at two points in a closed system andmeasures the flow in a direction perpendicular to the direction ofacceleration.

The scope of this invention is to be determined by the appended claims.

I claim:

1. A gas flow responsive instrument comprising two chambers, a mass ofrelatively hot gas in one of said chambers, a mass of relatively coldgas in the other of said chambers, a wall common to and between saidchambers and separating said masses, said wall being provided with apair of parallel slots, said slots being axially overlapping and spacedfrom each other, a pair of conductors, each said conductor having aresistance which is a function of the temperature of said conductor,each said conductor being adjacent to one of said slots and in athermally cooperating relationship with the temperature within saidslot, and means to measure the differential resistance of saidconductors.

2. An instrument as set forth in claim 1 including means to pass acurrent through said conductors to heat said conductors.

3. An instrument as set forth in claim 2 wherein said measuring meanscomprises a bridge circuit.

4. An instrument as set forth in claim 2 wherein means are provided tomaintain the temperature of said hot gas 7 I 6. An instrument adapted tomeasure acceleration, gravity and to determine verticals with respect tothe earth comprising two chambers, a relatively hot gas in one of saidchambers, a relatively cold gas in the other of said chambers, a wallcommon to and between said chambers and separating said gases, said wallbeing provided with a pair of gaps spaced from each other along thedirection of acceleration to be measured, a pair of conductors, eachconductor positioned in each of said gaps, each said conductor having aresistance which is a function of the temperature thereof, and means tomeasure the resistance differential of the said conductors.

7. An instrument as set forth in claim 6 wherein there are a pluralityof said apertures and conductors, each aligned in a different direction.

References Cited by the Examiner UNITED STATES PATENTS 2,455,394 12/1948Webber 735 14 X 2,552,017 5/1951 Schwartz et a1. 73204 FOREIGN PATENTS582,246 11/ 1946 Great Britain.

RICHARD C. QUEISSER, Primary Examiner.

DAVI-D SCHON BERG, Examiner.

1. A GAS FLOW RESPONSIVE INSTRUMENT COMPRISING TWO CHAMBERS, A MASS OFRELATIVELY HOT GAS IN ONE OF SAID CHAMBERS, A MASS OF RELATIVELY COLDGAS IN THE OTHER OF SAID CHAMBERS, A WALL COMMON TO AND BETWEEN SAIDCHAMBERS AND SEPARATING SAID MASSES, SAID WALL BEING PROVIDED WITH APAIR OF PARALLEL SLOTS, SAID SLOTS BEING AXIALLY OVERLAPPING AND SPACEDFROM EACH OTHER, A PAIR OF CONDUCTORS, EACH SAID CONDUCTOR HAVING ARESISTANCE WHICH IS A FUNCTION OF THE TEMPERATURE OF SAID CONDUCTOR,EACH SAID CONDUCTOR BEING ADJACENT TO ONE OF SAID SLOTS AND IN ATHERMALLY COOPERATING RELATIONSHIP WITH THE TEMPERATURE WITHIN SAIDSLOT, AND MEANS TO MEASURE THE DIFFERENTIAL RESISTANCE OF SAIDCONDUCTORS.